Many biologically active molecules contain sugar moieties which are optically active. For example, mammalian glycoaminoglycans (e.g., heparin, heparan sulfates, and dermatan sulfate) and aminoglycoside antibiotics (e.g., neomycin B, paromomycin, and lividomycin A) all contain L-ido sugars. See Lindahl, Pure & Appl. Chem., v. 69, 1897 (1997) and Fourmy et al., Science vol. 274, 1367 (1996). To facilitate the development of new therapeutic sugar-containing compounds, there is a need for simple methods of preparing optically pure sugars.